How does the bacterial transcription-coupling repair factor promote adaptive mutagenesis in Campylobacter jejuni?

空肠弯曲杆菌是一种引起食物中毒的细菌。许多用于食品生产的动物都被空肠梭菌所寄生，尽管这通常不会使动物生病。然而，当人类被感染时（例如，通过未经适当煮熟的受感染鸡肉），他们会患上腹泻，有时还会患上更严重的疾病。据估计，在像英国这样的发达国家，每年大约每100人中就有1人患有弯曲杆菌相关疾病。就损失的工作日数而言，这对社会来说是一项巨大的成本，对有关个人来说也是一种不适。大多数人在没有医疗干预的情况下从空肠梭菌感染中恢复过来，但当认为有必要治疗时，病人通常会被开一种叫做氟喹诺酮类的抗生素。氟喹诺酮类药物通过抑制细胞内的特定酶来杀死细胞，但如果细菌改变了编码这些酶的DNA序列，它们就会对抗生素产生抗药性。抗生素耐药细菌的日益流行对人类和动物健康都是一个日益严重的问题。当受到压力时，细菌有时会改变它们的生理机能，使它们的DNA比正常情况下突变得更快。虽然发生的大多数突变对细胞是有害的，但也有一些（比如那些赋予抗生素耐药性的突变）是有益的。因为细菌繁殖非常快，如果一个或两个个体获得突变，使它们能够在新环境中生存，它们将迅速成长为一个适应细菌的庞大种群。最近发现，空肠梭菌可以迅速发生突变，对氟喹诺酮类药物产生耐药性，因为当它遇到抗生素时，它会产生更多的一种名为Mfd的蛋白质。当C. jejuni暴露于其他抗生素时，增加突变频率的相同机制似乎也被使用，这可能是帮助C. jejuni适应环境极端变化的通用策略。了解这种适应策略是如何起作用的很重要，不仅可以让我们了解空肠梭菌对抗生素治疗的反应，还可以让我们了解它是如何适应我们对食物生产动物饲养环境的改变，或者发生突变导致更严重的疾病。Mfd蛋白增加突变率的发现是矛盾的，因为该蛋白最著名的是一种DNA修复蛋白，它可以防止细菌基因组中的突变。几年来，我们一直在研究一种叫做大肠杆菌的模式生物中的Mfd蛋白。我们已经对这种多功能蛋白质有了很好的了解，我们已经确定了这种蛋白质的许多改变形式，每一种都在单一功能上有特殊的缺陷。本提案工作的中心目标是应用这些知识来了解Mfd的过量生产如何增加C.空肠的突变率。我们将确定Mfd的哪些功能以及与之合作的哪些蛋白质在这一过程中是必需的，我们希望我们所获得的理解将有助于微生物学家通过开发避免或干扰突变产生途径的策略来控制空肠梭菌的突变率。

Campylobacter jejuni is a bacterium that causes food poisoning. Many animals that are raised for food production are colonised by C. jejuni, although this does not usually make the animals ill. However, when humans are infected (for example by infected chicken meat that has not been properly cooked) they can suffer from diarrhoea, and sometimes more serious illnesses. It is estimated that in developed countries like the UK about 1 in every 100 people suffer Campylobacter-related illness each year. This represents a large cost to the community in terms of lost working days, as well as discomfort for the individuals concerned. Most people recover from C. jejuni, infections without medical intervention, but when treatment is considered necessary the patients are often prescribed a class of antibiotics called Fluoroquinolones. Fluoroquinolones kill cells by inhibiting specific enzymes within the cell, but if bacteria change the sequence of the DNA that codes for these enzymes they can become resistant to the antibiotic. The increasing prevalence of antibiotic resistant bacteria is a growing problem for both human and animal health. When stressed, bacteria can sometimes change their physiology so that their DNA mutates more quickly than it would do normally. Although most of the mutations that occur will be detrimental to the cell, some (such as those that confer antibiotic resistance) will be beneficial. Because bacteria reproduce very quickly if one or two individuals acquire mutations that allow them to survive in a new environment they will rapidly grow into a substantial population of adapted bacteria. It has recently been discovered that C. jejuni can rapidly mutate to become Fluoroquinolone-resistant because when it encounters the antibiotic it makes more of a protein called Mfd. The same mechanism for increasing mutation frequency also seems to be used when C. jejuni is exposed to other antibiotics, and it may represent a universal strategy for helping C. jejuni to adapt to extreme changes in its environment. It is important to understand how this adaptive strategy works, not only so that we can understand how C. jejuni reacts to antibiotic treatment, but also so that we can understand how it might adapt to changes that we make in the environment that food-producing animals are reared in, or mutate to cause more serious disease. The finding that the Mfd protein increases the mutation rate is paradoxical, because the protein is best known as a DNA repair protein that prevents mutations arising in bacterial genomes. For several years we have been studying the Mfd protein in a model organism called Escherichia coli. We have gained a good understanding of this multi-functional protein, and we have identified many altered forms of the protein, each of which is specifically defective in a single function. The central aim of the work in this proposal is apply this knowledge to understand how overproduction of Mfd increases the rate of mutation in C. jejuni. We will identify which functions of Mfd, and which of the proteins that it cooperates with, are needed for the process, and we hope that the understanding that we gain will help microbiologists to control the rate of mutation of C. jejuni by developing strategies that avoid or interfere with the mutation-generating pathway.